Question

Solve..............
(85+90+95+............ +415)

Answer 1

HELLO DEAR,

85 + 90 + 95 + .........415

.a = 85 ,
D = 90 - 85 = 5
L = 415

l = a + (n - 1)d

=> 415 = 85 + (n - 1)5

=> 415 - 85 = (n -1)5

=> 330 = (n - 1)5

=> n - 1 = 66

=> n = 66 + 1

=> n = 67

now,

We know that:-

Sn = n/2(a + l)

=> 67/2(85 + 415)

Sn = 67/2×500

=> SN = 67 × 250

=> Sn = 16750

I HOPE ITS HELP YOU DEAR,
THANKS

Answer 2

Heya..!!!


We know that:-

l = An = a + (n - 1)d

AND,

Sn = n/2(a - l)


Now,

Ap: 85 + 90 + 95+...... 415

a = 85,
D= 90 - 85 = 5
L = 415


L = a + (n - 1)d

=> 415 = 85 + (n - 1)×5

=> 415 - 85 = (n - 1)5

=> 330/5 = n - 1

=> n = 66 + 1 = 67

Sn = n/2(a + l)

=> Sn = 67/2(85 + 415)

=> Sn = 67/2(500)

= 67 × 250..


=> Sn = 16750
.